Electronic device for maintenance of the oscillations of a balance wheel

ABSTRACT

In an electronic device for maintenance of the oscillations of the balance wheel of a timepiece comprising an astable multivibrator supplying current pulses to a coil which is electromechanically coupled with the balance wheel, a negative feedback circuit is provided to avoid a saturation of the astable multivibrator: a new improved and more simple device is provided to avoid this saturation so as to be compact in structure and integrated easily manufactured by integrated circuit techniques.

United States Patent [191 Scherrer 1 Get. 29, 1974 ELECTRONIC DEVICE FOR 3,701,052 10/1972 Keller 58/23 AC MMNTENANCE OF THE ()SCKLLATIONS 3,705,362 [2/1972 Keller et al. 331/108 A OF A BALANCE WHEEL [75] Inventor: Igor Scherrer, Colombier,

Switzerland [73] Assignee: Ebauches S.A., Neuchatel,

Nevenburg, Switzerland [22] Filed: Mar. 28, 1973 [21] Appl. No.: 345,687

[30] Foreign Application Priority Data Mar. 28, 1972 Switzerland 4569/72 [52] US. Cl 58/28, 58/23 R, 58/23 A [51] Int. Cl. G04b 17/00 [58] Field of Search 318/119, 126, 129, 130; 331/116 M, 108 A; 58/23 R, 23 A, 23 AC, 23 D, 23 TE, 23 V, 28 B, 28 D, 28 R [56] References Cited UNITED STATES PATENTS 3,530,662 9/1970 Schoninger 331/116 M Primary Examiner-Richard B. Wilkinson Assistant Examiner-U. Weldon Attorney, Agent, or Firm-lmirie, Smiley & Linn [57] ABSTRACT In an electronic device for maintenance of the oscillations of the balance wheel of a timepiece comprising an astable multivibrator supplying current pulses to a coil which is electromechanically coupled with the balance wheel, a negative feedback circuit is provided to avoid a saturation of the astable multivibrator: a new improved and more simple device is provided to avoid this saturation so as to be compact in structure and integrated easily manufactured by integrated circuit techniques.

3 Claims, 2 Drawing Figures PAIENTEUUCTZSISH 844 5 FIGA I ELECTRONIC DEVICE FOR MAINTENANCE OF THE OSCILLATIONS OF A BALANCE WHEEL BACKGROUND OF THE INVENTION This invention relates generally to electronic devices for maintenance of the oscillations of a balance wheel and more particularly to electronic devices of the type in which a negative feedback circuit is provided to avoid saturation of the transistor drive network. The negative feedback circuits in the known devices are generally complicated in structure and it is very difficult to manufacture them in the form of an integrated circuit.

SUMMARY OF THE INVENTION Accordingly an object of this invention is to provide an electronic device of the described type with a new and improved negative feedback circuit to avoid saturation of the astable multivibrator.

Another object of this invention is to provide a new negative feedback circuit used in an electronic device of the described type which can be easily manufactured in form of an integrated circuit.

The electronic device for maintenance of the oscillations of the balance wheel according to this invention comprises a negative feedback circuit having at least a transistor connected into the base circuit of the input transistor and being a part of a current generator. The base current of the input transistor can be varied according to the potential appearing at the terminal which is common to the coil and to the output transistor so that the output transistor will never be saturated in static running.

BRIEF DESCRIPTION OF THE DRAWINGS The above objects, features and advantages of this invention will become apparent from the following detailed description of the illustrative embodiments shown in the accompanying drawings.

FIGS. I and 2 show two embodiments of the device according to this invention.

DESCRIPTIONOF THE EMBODIMENTS I tween the positive terminal of the voltage source and the collector of the output transistor T which applies a current pulse to the coil 4. Further, the coil 4 is electromechanically coupled to a balance wheel 9 of a timepiece in such a manner that the magnetic field created by the current flow through the coil gives driving pulses to the balance wheel. Such a coupling is shown for example, in FIG. 3 of US. Pat. No. 3,238,431 and illustrated schematically in FIGS. I an 2 herein. The terminal which is common to the coil 4 and the output transistor T is indicated by the reference letter B. The capacitor 3 is connected between the terminal B and the base of the input transistor T and a negative feedback resistor 5 is connected between the terminal B and the collector of a transistor T of which the base is connected to the collector as to form a diode.

The transistors T and T form a controlled current generator and may be realized in an integrated circuit.

The embodiment of FIG. 1 distinguishes from the known embodiments by the elements T T and 5 con nected between the base of the input transistor T, and the negative terminal of the power source, these elements taking the place of a resistor as generally provided in prior circuits.

The operating mode of the multivibrator of the coil 4 and the balance wheel is known. The current l has to be considered as coming from a current generator: the ratio 1 is equal to the ratio of the surface of the transistors T and T The respective base-emitter voltage of each of the transistors T and T is the same in value: in this case the base current is proportinal to the surface through which it can have a path, because the specific conductivity value is the same for both of the PN-junctions. If both transistors T and T are formed on the same substrate and at the same time near by each other, but with different surfaces, all the working conditions namely the temperature, the doping of the different layers, etc., are the same so that the collector-current ratio will be equal to the ratio of the transistor surfaces. In the expression 4 b 2" VBE4 s where R is the resistance of the coil 4, V the baseemitter Voltage of the transistor T and R the value of the resistor 5, it becomes apparent that when l increases, the potential at the point B becomes lower so that 1., and consequently I become lower too. This decreasing of l is opposed to an increase of I and a state of equilibrium is obtained before T is saturated. In the dynamic operation mode a primary difference between this device and the known devices consists in that the condenser 3 is charged through a current generator and not through a resistor, with the advantageous result that becomes zero during each pulse applied to balance wheel 9.

By the static negative feedback effect between the common terminal B and the input transistor T, a static saturation of the output transistor T is avoided.

In the embodiment of FIG. 2, which can be easily manufactured as an integrated circuit the current generator is formed by the transistors T T T and T the negative feedback resistor 5 being connected between the common terminal B and the transistor T, which controls the transistor T This transistor T is seriesconnected with a resistor 8. The transistor T is a part of the current generator and the current 1;, is the product of I with the ratio of the surface of the transistors T and T Practically,for the foreseen uses, the value of the resistor 8 can be in order of 10 K0, and this resistor can be integrated with the required accuracy. The value of the resistor 5 is not critical and can be integrated too in spite of the relatively high value of about When the potential at the common terminal B decreases sufficiently, the transistor T becomes conducting, the potential at the base of the transistor T increases and the current generator is blocked. Saturation of the transistor T is thus avoided.

Though the device of FIG. 2 appears complicated off-hand, its realization is simplified by complete integration of the elements which compose the negative feedback circuit.

What is claimed is:

I. An electronic device for maintenance of the oscillations of a balance wheel of a timepiece, comprising:

a multivibrator including an input transistor and an output transistor, the base of said input transistor and the collector of said output transistor being connected by a capacitor, said multivibrator producing pulses at the collector of said output transistor; a source of operating potential; a coil connected between said potential source and the collector of said output transistor and electromechanically coupled to the balance wheel, said coil receiving applied pulses from said output transistor of said multivibrator for maintaining the periodic oscillations of the balance wheel; and negative feedback means connected at its input to the junction of said coil and the collector of said output transistor and providing an output control signal to the base of said input transistor, said negative feedback means comprising controlled current generator means in the form of a transistor, the collector of which is directly connected to the base of said input transistor for supplying said output control signal to said base of said input transistor, said negative feedback means further comprising controlling network means connected at an input to the junction of said coil and said output transistor and connected at an output to the base of said controlled current generator transistor, said controlling network means being responsive to a decrease in the potential appearing at said junction for controlling said current generator means to provide a decreased amount of current to said input transistor thereby preventing said output transistor from becoming saturated during operation, said controlling network means including at least one active element in the form of another transistor having its base and collector electrodes connected together to function as a diode, said base electrode connected to said base electrode of said controlled current generator transistor and further coupled to said input of said negative feedback means.

2. An electronic device as claimed in claim 1, wherein said controlling network means comprises a resistor, and said interconnected electrodes of said one active element being connected to one side of said resistor and to the base of said current generator transistor; and wherein the other side of said resistor is coupled to said junction between said coil and said output transistor.

3. An electronic device as claimed in claim 1, wherein said controlling network means comprises: a first transistor, the base of which is connected through a first resistor to said junction point between said coil and said output transistor; a second transistor, a third transistor, and a fourth transistor, said second transistor having its collector and emitter electrodes connected with the collector and emitter electrodes, re-

spectively, of said first transistor, and having its base and collector electrodes connected together to the collector of said third transistor, a second resistor connected between said source of operating potential and the emitter of said fourth transistor, the collector of said fourth transistor being connected to said interconnected electrodes of said active element, whereby said first transistor is connected as a variable resistance in parallel with the emitter-collector circuit of said second transistor, the base of which is connected to the base of said fourth transistor to control its base potential, and the bases of said active element and said third transistors being connected together to the base of the transistor forming said current generator. 

1. An electronic device for maintenance of the oscillatioNs of a balance wheel of a timepiece, comprising: a multivibrator including an input transistor and an output transistor, the base of said input transistor and the collector of said output transistor being connected by a capacitor, said multivibrator producing pulses at the collector of said output transistor; a source of operating potential; a coil connected between said potential source and the collector of said output transistor and electromechanically coupled to the balance wheel, said coil receiving applied pulses from said output transistor of said multivibrator for maintaining the periodic oscillations of the balance wheel; and negative feedback means connected at its input to the junction of said coil and the collector of said output transistor and providing an output control signal to the base of said input transistor, said negative feedback means comprising controlled current generator means in the form of a transistor, the collector of which is directly connected to the base of said input transistor for supplying said output control signal to said base of said input transistor, said negative feedback means further comprising controlling network means connected at an input to the junction of said coil and said output transistor and connected at an output to the base of said controlled current generator transistor, said controlling network means being responsive to a decrease in the potential appearing at said junction for controlling said current generator means to provide a decreased amount of current to said input transistor thereby preventing said output transistor from becoming saturated during operation, said controlling network means including at least one active element in the form of another transistor having its base and collector electrodes connected together to function as a diode, said base electrode connected to said base electrode of said controlled current generator transistor and further coupled to said input of said negative feedback means.
 2. An electronic device as claimed in claim 1, wherein said controlling network means comprises a resistor, and said interconnected electrodes of said one active element being connected to one side of said resistor and to the base of said current generator transistor; and wherein the other side of said resistor is coupled to said junction between said coil and said output transistor.
 3. An electronic device as claimed in claim 1, wherein said controlling network means comprises: a first transistor, the base of which is connected through a first resistor to said junction point between said coil and said output transistor; a second transistor, a third transistor, and a fourth transistor, said second transistor having its collector and emitter electrodes connected with the collector and emitter electrodes, respectively, of said first transistor, and having its base and collector electrodes connected together to the collector of said third transistor, a second resistor connected between said source of operating potential and the emitter of said fourth transistor, the collector of said fourth transistor being connected to said interconnected electrodes of said active element, whereby said first transistor is connected as a variable resistance in parallel with the emitter-collector circuit of said second transistor, the base of which is connected to the base of said fourth transistor to control its base potential, and the bases of said active element and said third transistors being connected together to the base of the transistor forming said current generator. 